A245991 Number of length n+2 0..4 arrays with no pair in any consecutive three terms totalling exactly 4.

64, 208, 676, 2196, 7132, 23168, 75260, 244464, 794096, 2579500, 8379052, 27217860, 88412560, 287192948, 932896352, 3030352272, 9843575108, 31975148500, 103865731612, 337389844512, 1095952482460, 3560011839440, 11564081956784

Offset: 1

Author

R. H. Hardin, Aug 09 2014

Keywords

• nonn

Examples

			Some solutions for n=7:
  3  3  4  0  2  2  3  2  2  3  4  3  4  0  4  0
  4  4  1  3  1  1  4  3  4  2  2  0  1  3  2  1
  4  4  1  0  1  1  3  4  4  3  4  2  2  2  1  1
  4  2  2  2  0  4  4  3  2  3  3  0  0  3  4  2
  3  4  0  0  2  2  3  3  1  0  2  1  3  4  4  4
  3  3  0  3  0  1  2  3  4  0  4  2  3  3  3  4
  2  3  0  0  1  1  0  0  2  2  1  1  0  2  4  4
  4  0  3  0  1  2  3  0  1  3  2  4  2  3  4  4
  4  0  2  1  1  4  0  3  0  4  1  1  1  0  2  4
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..210

Crossrefs

Column 4 of A245995.

Formula

Empirical: a(n) = 2*a(n-1) + a(n-2) + 9*a(n-3) + 3*a(n-4).

Empirical g.f.: 4*x*(16 + 20*x + 49*x^2 + 15*x^3) / (1 - 2*x - x^2 - 9*x^3 - 3*x^4). - Colin Barker, Nov 05 2018